The present invention relates to the field of locating terminals connected to a cellular telecommunications network. It particularly relates to a locating method which makes use of a history of cells visited by a terminal.
This method is particularly advantageous in the case of terminals with a UICC card (“Universal Integrated Circuit Card”) which stores this history.
“UICC card” is understood to mean any card comprising a microcontroller and memory. It can be used in mobile phones to store information specific to the subscriber to a mobile network. The ETSI TR 102 216 standard specifies the details of such a UICC card. A UICC card may comprise a SIM (“Subscriber Identity Module”), USIM (“Universal Subscriber Identity Module”), or ISIM (“IP Multimedia Services Identity Module”) application.
The term “cell” is understood to mean a geographical area covered by at least one antenna of a network, for example for mobile telephony. Typically, a cell is covered by a base station which has at least one antenna to which terminals of said network are connected. The network is, for example, a GSM (“Global System for Mobile communications”) mobile network, or UMTS (“Universal Mobile Telecommunications System”), or LTE (“Long Term Evolution”).
With the proliferation of terminals equipped with dedicated GPS (“Global Positioning System”) location systems, these terminals are now quite common; however, there are still many applications where it is not relevant to integrate such dedicated systems into the terminals. Payment terminals, low-cost mobile phones, a smart card comprising a UICC card, or various other connected devices are connected to a cellular telecommunications network but do not have components dedicated specifically to determining their location, particularly due to the size and cost of such components.
The ability to locate a terminal remains a very popular option, however, regardless of the intended application of the terminal. Typically, this option can help find a mislaid device. In addition, a cellular network operator may wish real-time knowledge of the geographical distribution of the various terminals connected to its network. This can, for example, allow it to dynamically calibrate the network equipment it manages in order to accommodate variations in the network load within a given territory.
Some network parameters available in a terminal can be used to locate the terminal. Typically, the identifier of the cell where the terminal is located is accessible in a terminal connected to a cellular network and can be used to locate the terminal.
In particular, when the terminal moves from one cell to a neighboring cell, the identifier of the new cell is quickly available at the terminal. The term “handover” is used for the transfer between cells when the terminal moves from one cell to another, whether or not a communication is in progress during the transfer.
Typically, the identifier of the cell is sent in “broadcast” mode, by the base station covering the cell. The channels used for transmission of this identifier are SCH-type synchronization channels. P-SCH (Primary Synchronization Channel) or S-SCH (Secondary Synchronization Channel) channels are typically used to send the cell identifier in a UMTS network.
The cell in which the terminal is located at a certain moment is called the “current cell”.
The terminal can then retrieve location coordinates of this current cell using the cell identifier. To do this, it sends a request containing the identifier of the current cell to a server hosting a repository of cell identifiers. This repository of cell identifiers stores location coordinates for each cell identifier. A response to the request is then returned from the server to the terminal, containing the location coordinates for the current cell.
From these location coordinates of the cell, the terminal can determine its approximate location. Typically, the terminal determines that it is located in the vicinity of the location coordinates of the current cell. These location coordinates of the current cell frequently correspond to the location coordinates of the base station covering the current cell.
However, this solution is not satisfactory in terms of reliability. In many situations detailed below, it is impossible to retrieve the location coordinates of the current cell.
It is, for example, possible that the repository of cell identifiers has not been updated with the identifiers of all cells in the network. As new base stations are deployed in the network, many new cells are created and the repository is not updated in real time.
It is also possible for a mobile antenna to be deployed to cover an exceptional event. This event-specific mobile antenna serves as a temporary base station. However, the mobility of this temporary base station makes it impossible to keep the repository updated with the location coordinates for the identifier associated with this temporary base station. The cell identifier transmitted by this event-specific mobile antenna may therefore not be associated with location coordinates that actually correspond to the temporary location of the antenna.
The terminal may also have problems retrieving the identifier of the current cell. This situation can occur, for example, when the quality of service (QoS) of the transmission between the terminal and the base station covering the current cell is very poor, and in particular the transmission through the P-SCH and S-SCH channels in the case of a UMTS network. In this situation, it is possible that the frames sent by the base station to the terminal and containing the identifier of the current cell are not properly transmitted and therefore cannot be decoded by the terminal.
In these situations where it is impossible to retrieve location coordinates for the current cell, no location information is available. No terminal location information can therefore be provided to a user. Thus, at a given moment, if the location coordinates for the current cell are not available, the user does not have access to any location information.